1. Field of Invention
The invention relates to a fuel cell power generation system and a control method thereof.
2. Description of Related Art
There is a fuel cell power generation system disclosed in Japanese Laid-Open Patent Publication No. 6-295735, in which the power source of accessories that operate using commercial power in normal state is switched from a commercial power supply to a fuel cell upon detection of a failure in commercial power. In this system, power is supplied to accessories which are used for operating the fuel cell power generation system from the commercial power supply upon start-up. When the output of the fuel cell reaches a rated level, the power source of some of the accessories is switched to the fuel cell from the commercial power supply. With this system, upon detection of the power failure of the commercial power supply, the power source of those accessories powered by the commercial power (i.e. the accessories not already switched to the fuel cell) is switched to the fuel cell so as to cope with the power failure.
The aforementioned fuel cell power generation system, however, does not perform a control for supplying power in accordance with the power required by the accessories from the fuel cell in case of power failure which is typically lower than the power required in the absence of a power failure. Therefore, the fuel cell is unnecessarily operated and consumes an excessive amount of fuel, resulting in reduced efficiency of the system. Even if the fuel cell is brought into an operating state at the rated output, the commercial power source is still used to supply power to some of the accessories. Accordingly, in case of power failure in the commercial power source, the power source to some of the accessories has to be switched to the fuel cell so as to cope with the power failure.